This invention relates to a device for indicating the degree of tilt of a vehicle headlamp beam and, more specifically, to a device having a bubble level formed by a liquid-filled vial with a gas bubble therein that coacts with a graduated scale to indicate the degree of tilt of the vial from horizontal.
Such an indicating device typically is mounted on the frame or other component of the headlamp assembly. At the vehicle assembly plant, the frame is tilted about a horizontal axis to establish proper aim of the headlamp beam in a vertical direction. Once this is achieved, the indicating device is calibrated in order to "zero" the bubble and establish the preset position of the headlamp. If the headlamp subsequently becomes improperly aimed, the indicating device may be used to determine when the lamp has been adjusted back to the preset position.
The vial of the bubble level usually is molded of plastic and, after being filled with liquid, is closed by a plastic cap. The vial is transparent in order to enable viewing of the bubble and the scale.
Use of a bubble level as a means for indicating the angle of inclination from true level has an inherent degree of inaccuracy. In large, the problem resides in interpreting where the peripheral edge of the bubble lies. The meniscus formed by the surface tension of the fluid against the wall of the vial results in a visual thickness of the peripheral edge of the bubble. This thickness can result in erroneous readings, even when gauging the bubble position between a scale and the fore and aft region of the bubble, Also, there usually is a poor visual contrast between the liquid and the bubble. As a result, even estimating the center of the bubble becomes difficult.